The linear model is a multi-channel attribution model and is the simplest of the multi-channels to calculate. Every touchpoint in the path to conversion is counted and given an equal weighting. For instance, if there were 5 touchpoints with different channels, each touchpoint/channel would be credited 20%. An example of this linear attribution weighting can be found in the chart below.
Depending on the business and acquisition strategy, this can be a useful model, but it does have some drawbacks. If each of your channels does an equal amount of the heavy lifting to create a conversion, the linear model is perfect; however, if you have channels that do more "work" than other channels, linear attribution (while more accurate than last touch) can be misleading. For example, if your acquisition strategy is heavily front loaded with an intensive lead generation channel, such as trade shows but it also uses email campaigns that lead to conversions. In this instance if it took 9 emails before a conversion, the tradeshow channel would only receive 10% of the credit, even though you may feel it did 40% of the work.